Vertical axis wind turbines (VAWT) are a promising alternative renewable energy source. Recent innovations involve reducing operation noise, active flow control and complexity. VAWT can extract power regardless of flow direction (Alam & Iqbal, 2009).
Darrieus Wind TurbineFeng et al. carried out wind tunnel test on a Darrieus wind turbine with and without an optimal power controller. They maximised turbine efficiency by matching rotor and generator.
Gorelov (2009) stated that the Darrieus rotor type is analogous to a flapping wing. The torque on the rotor shaft is from pulsed forces acting on the blades. Aerodynamic calculations would involve nonlinear airfoil theory under turbulent flow.
Self-Start TurbinesDebate exists between designers for whether turbines can start unaided. Hill et al. simulated starting of an H-rotor Darrieus turbine under steady wind. They also performed wind tunnel experiment using a prototype to varied results. This indicated there are still gaps in aerofoil characteristics for an accurate model.
Ferreira et al. investigated dynamic stall at various tip speed ratios. Dynamic stall occur for low tip speed ratio to affect loads and power. The Netherlands scientists carried out 2D particle image velocimetry (PIV) to find a relationship between the blade angle, perceived velocity and Reynolds number. The results showed how air circulates for a small urban wind turbine.
Future DevelopmentMiller et al. developed Sistan windmills modern adaptations. Sistan windmills are drag-force type energy generators for buildings. They experimented with a scale model to achieve more than 40% efficiency.
Takahashi et al. are developing a suitable generator for low-speed vertical wind turbines for urban installation. This generator is coreless and has radial magnetic flux. The magnets and coils are on the outer end of the device. The design has a high speed of flux change and output voltage. The generator power at 283 W maximum would be independent of its diameter. The generator is able to self-start at wind around 1 m/s.
Alam, M.J. & Iqbal, M.T. (2009). Design and development of hybrid vertical axis turbine. Canadian Conference on Electrical and Computer Engineering. 1178-1183.
Feng, G., Liu, Z., Daorina, B. & Gong, Z. (2009). Experimental research on vertical axis wind turbine. Asia-Pacific Power and Energy Engineerign Conference.
Ferreira, C., van Kuik, G., van Bussel, G. & Scarano, F. (2009). Visualization by PIV of dynamic stall on a vertical axis wind turbine. Experiments in Fluids, 46(1), 97-108.
Gorelov, D. N. (2009). Analogy between a flapping wing and a wind turbine with a vertical axis of revolution. Journal of Applied Mechanics and Technical Physics, 50(2), 297-299.
Hill, N., Dominy, R., Ingram, G. & Dominy, J. (2009). Darrieus turbines: The physics of self-starting. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 223(1), 21-29.
Miller, G., Jentsch, M. F. & Stoddart, E. (2009). Vertical axis resistance type wind turbines for use in buildings. Renewable Energy, 34(5), 1407-1412.
Takahashi, T., Yasuda, Y., Ohmoto, S. & Hara, T. (2009). Proposal and development of radial air-gap coreless generator suitable for small wind turbine used in urban area. Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi), 167(1), 26-34.
Wilks, N. (2009). Windy city [vertical-axis wind turbines]. Environmental Engineering, 22(1), 24-25.